Screw propeller



Sept. 2, 1947. F. w. PAWLOWSKI 2,426,742

SCREW PROPELLER Filed Nov. 20, 1945 2 Sheets-Sheet l IINIVENTOR Sept. 2,1947. F. w. PAWLOWSKI 2,426,742

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Patented Sept. 2, 1947 UNITED STATES PATENT )FFICE SCREW PROPELLER FelixW. Pawlowski, Ann Arbor, Mich.

Application November 20, 1943, Serial No. 511,192

2 Claims. 1

This invention relates to propellers and more particularly to animproved propeller of the screw type.

One of the objects of the present invention is to provide a propellerhaving greater efliciency, or greater output of energy for a given inputthan it is possible to obtain with conventional screw propellers.

Another object of the present invention is to provide a propeller whichcan absorb and deliver greater power for its given diameter than can beabsorbed and delivered by a conventional propeller of an equal diameter.

A further object of the present invention is to provide a screwpropeller having greater rigidity and strength than conventionalpropellers of a corresponding description.

A still further object of the present invention is to provide animproved screw propeller with the aid of which it is possible toincrease the cruising radius and the speed of .various crafts, at thesame power consumption or fuel supply as would be possible with aconventional propeller.

A still further object of the present invention is to provide animproved screw propeller havin greater rigidity and strength.

A still further object ofthe present invention is to provide a more safepropeller less dangerous to persons who by accident may come close tothe tips of the rotating blades.

It is an added object of the present invention to provide an improvedscrew propeller of the foregoing character which is simple inconstruction, dependable in operation, and is relatively inexpensive tomanufacture.

Other objects and advantages of the present invention will be apparentfrom the following description and the appended drawings forming a partof the present specification, in which drawings similar numerals referto similar parts throughout the several views.

Fig. l is a rear view of a screw propeller embodying the presentinvention.

Fig. 2 is a sectional view of the propeller of Fig. 1, said view takenin the direction of the arrows on the section'planes passing through thebroken line 2-2 of Fig. 1.

Fig. 3 is a view taken radially and inwardly on one of the blades of apropeller similar to the one shown in Figs. 1 and 2 but having a twistedblade.

Fig. 4 is a view similar in part to Fig. 3 and showing a blade of adifferent cross section.

Fig. 5 is a rear view of a modified screw propeller embodying thepresent invention.

Fig. 6 is a sectional view taken in the direction 2 of the arrows on thesection plane passing through the section line 6-6 of Fi 5.

Fig. '7 is a side view of one of the blades used in propellers embodyingthe present invention.

Fig. 8 is an end view, partly in section, of the blade shown in Fig. '7.

Fig. 9 is a side view of one of the blades of another type used in thepropellers embodying the present invention.

Fig. 10 is an end view, partly in section, of the blade shown in Fig. 9.

Fig. 11 is a rear view of still another modified propeller embodying thepresent invention.

Fig. 12 is a sectional view taken in the direction of the arrows on linel2l2 of Fig. 1'1.

Before explaining in detail the present invention, it is to beunderstood that the invention is capable of other embodiments andmodifications and that the terminology and phraseology employed hereinis for the purpose of description and not of limitation, and it is notintended to limit the invention beyond the requirements of the priorart.

It is also to be understood that the term screw propeller as herein usedrefers to devices including a number of elements or blades so positionedwith respect to their axis of rotation, that their rotation in a fluidmedium, gas or liquid, produces a thrust in the direction perpendicularto the plane of rotation, which thrust is utilized to propel or movevarious crafts and other instrumentalities carrying such screwpropellers. This term, as herein employed, does not refer to deviceshaving different transformation of forces or energy, such, for instance,as devices in which the movement of liquid is utilized to developrotative energy, such as water turbines. The term streamline as hereinemployed refers to aerofoils or shapes having well rounded leading edgesand substantially sharp trailing edges, with connecting surfaces beingstraight, convex or concave.

In the drawings there are shown, by way of example, a number of screwpropellers embodying the present invention. Referring particularly tothe construction shown in Figs. 1 and 2, the construction illustratedtherein comprises a substantially streamline hub 20 which is adapted tobe drivingly connected in any suitable way to a driving shaft. To saidhub 20 there are connected, in any suitable manner, a plurality, in thepresent instance three, of blades 2|. The blades 2] have a streamlinecross section which is substantially uniform throughout the effectivelength of the blades, the uniformity of the cross section the blade, asshown in Fig. 2, or vary in any desirable manner, such as illustrated inFigs. 3 I

and 4.

To the outer extremities or tips of the blades 2| there are connected aplurality of substantially round plates 22 of streamline cross section,which plates are adapted to obstruct and thereby to eliminate in amaterial degree the objectionable flow of the fluid from the highpressure sides to the low pressure sides of said blades in operation ofthe propeller. By virtue of the above-construction the loss of energydue to the above flow, which loss is usually referred to in the art asthe tip loss, is substantially eliminated and the efficiency of thepropeller is greatly increased. By making plates 22 of streamline crosssection, the resistance of the fluid to the motion of said plates 22therethrough is greatly reduced, and the loss of energy due to it isbrought to the point where it is greatly overbalanced by the gain due tothe elimination of the tip losses.

Referring to the construction illustrated in Figs. 5 and 6, the screwpropeller illustrated in said figures comprises a hub 30 which issimilar to the hub 20 of the construction shown in Figs. 1 and 2. Tosaid hub 30 there are'connected, in any suitable manner, a plurality, inthe present instance six, of blades 3|. In this construction it ispreferred to use more than four blades, six being one of the preferablenumbers, although the use of higher number of blades, such, forinstance, as ten or twelve may be still more desirable in certaininstances. The ratio of the length to the width of the blade, in myimproved propeller, is greater than 3 to 1, the ratio of 6 to lbeing oneof the preferred ratios for average conditions, still greater ratiosbeing desirable for special conditions. By decreasing the width andincreasing the number of the blades 9. much greater efliciency of thepropeller is attained.

The blades 3| are of streamline cross sections as shown in Fig. 8, thewidth of the blades being substantially uniform, as shown in Fig. '7.Under certain conditions it may be desirable to use blades withoutwardly'decreasing width, and to have the angle of each individualblade with respect to the plane of its rotation gradually changing alongits length. It should be understood, however, that while in conventionalpropellersthe width of a blade changes along the radius of a propellerrather abruptly, the width of a blade in my improved propeller changesvery slightly, making both the leading and the trailing edges of a bladestraight, or nearly straight lines, thereby eliminating considerablecurvature which is common in many types of conventional propellers.

Means are provided to obstruct the flow of fluid from the high pressuresides to the low pressure sides of the blades. In the present embodimentof the invention said means are in the form of a circular rim 32concentric with the hub and connected to the tips of the blades in anysuitable manner. The rim 32 is of a streamline cross section, and itswidth should be suflicient to form a substantial obstruction to the tipflow of the fluid. It is preferable to have the rim of such a width thatit overhangs the leading and the rim is greatly' amplified.

- 4 trailing edges of the blades. By virtue of providing a continuousrim connecting the tips of all blades, the tip losses in the propellerare great-- ly reduced, and the structure of the propeller is madestronger.

For the proper understanding of the present invention, it is extremelyimportant to understand that the rim 32 of my improved propeller. is nota shroud pr a conical ring, or blade tying hoop, many designs of whichhave heretofore been proposed in connection with screw propellers. Whilenarrow hoops have been tried merely to strengthen propellers or toprevent flutter of the blades, various conical rings and shrouds havebeen proposed 'with the expectation that they would produce a compactcolumn of fluid and would direct such a column of fluid at an increasedspeed against the propeller blade and would thus enable developing-morepower. How: ever, in order to cause the fluid to converge toward thepropeller blades, such shrouds cause separa- -tion of fluid from theopposite surface of the shroud, and the vacuum so produced causesserious drag on the propeller. Such drag is substantially equal to or isgreater than the increase in the useful thrust of the propeller, andtherefore no net increase in power is realized. In other words, theamount of power or energy which is spent for effecting such convergenceof fluid toward the propeller blades is equal or greater than the amountof power or energy gained at the blades, and therefore no additionalpower or energy is thus gained by the use of such devices.

The rim 32 of my improved propeller is so dewith the present inventionmore safe, since it reduces greatly the danger to persons who byaccident may come close to the tips of the rotating blades, such aspeople overboard or life-boats in cases of marine propellers, orparachutists and attending personnel in cases, of aircraft propellers.

By staggering the blades either at their roots or at their tips, thestrengthening function of the It is preferable to stagger the blades attheir roots, and such a construction is shown in Figs. 11 and 12.Referring to said figures, said structure comprises an elongated,substantially streamline hub 40, a plurality of blades 4| connected tosaid hub, and a rim 42 connected to the tips of the blades H. Theconstruction and operation of this particular propeller, with theexception of the staggered arrangement of the blades and the resultingincreased strength, is substantially similar to that shape, theefiiciency of the propeller, and its strength, are greatly increased,and the objects of this invention, and a number of additional advantagesare attained.

I claim:

1. In a thrust producing screw propeller, a plurality of blades in anumber greater than four, in said blades the ratio of the length of theblade to its width being at least 6, each of said blades having astraight well rounded leading edge and a straight sharp trailing edge,the cross section of each of said blades being dimensionally uniformthroughout the length of the blades, said blades being set to haveuniform pitch throughout their lengths; and a circular rim encirclingthe tips of said blades and connected thereto, said rim havingsufiicient width to ensure its substantial overhanging both the leadingand the trailing edges of the blades, said rim having its front edgewell rounded and its rear edge sharp, the plane connecting the extremelines of said rim edges around the entire rim forming a cylindricalplane co-axial with the propeller.

2. A construction as defined in the preceding claim 1, the blades beingmade of rolled stock.

FELIX W. PAWLOWSKI.

a file of this patent:

UNITED STATES PATENTS Number Name Date 1,467,515 Stewart 1 Sept. 11,1923 1,539,273 Reed May 26, 1925 1,622,222 Caldwell Mar. 22, 1927506,572 Wagener Oct. 10, 1893 1,518,502 Gill Dec. 9, 1924 859,089 LowryJuly 2, 1907 1,033,662 Blake July 23, 1912 2,014,032 Sharpe et al Sept.10, 1935 1,067,385 Taylor July 15, 1913 1,954,437 Washburne Apr. 10,1934 2,097,389 I DeMey Oct. 26, 1937 2,313,413 Weske Mar. 9, 1943FOREIGN PATENTS Number Country Date 175,922 Great Britain May 2, 1922370,500 Italy Apr. 18, 1939 2,188 Great Britain 1862

